From MythTV Official Wiki
This page is up-to-date to MythTV version 0.20
- X-Video Motion Compensation (XvMC) XvMC can greatly reduce CPU utilization when playing back MPEG-2 video. In theory it should also reduce bus bandwidth requirements. Savings will be most dramatic with slow CPUs or when playing HDTV. SDTV will benefit as well, but most modern CPUs can already play back SDTV without XvMC. MythTV can be compiled to use XvMC for native playback. External players such as Xine and Mplayer can also be compiled to support XvMC.